Recently, increasing attention has been paid to 3D display devices. Such 3D display devices are classified into a stereoscopic type using a binocular parallax method, an integrated image type, a holographic type, a volumetric 3D display type, and the like according to the implementation methods. Among these types, the stereoscopic type display devices are divided into a glass type using glasses to implement 3D display and a non-glass type using no glasses. In general, the type of implementing the 3D display without glasses is called an auto-stereoscopic 3D display, which includes a multi-view display and an integrated video display.
With respect to non-glass 3D display device. In order to support both 2D video and 3D video, the display device needs to be implemented in a form of capable of selecting 2D and 3D modes. In order to implement this form, various techniques have been developed. One of the techniques is to form, on a 2D display, a lens array structure that is actively driven as a lens only when a viewer views a 3D image. As representative techniques for realizing such an active lens, there area method using an electrowetting effect and a method using an electro-optic effect of a liquid crystal.
In the case of a multi-view 3D display using a lens array, a 3D image can be implemented with almost no reduction in luminance. In the case of implementing only horizontal parallax, a 1D array of microlenses is applied. In the case of implementing horizontal parallax and vertical parallax, a 2D array of microlenses is applied.
As described above, among the active liquid crystal lens techniques that can be used for a 2D/3D switchable display device capable of selecting one of 2D and 3D, there is a polarization dependent liquid crystal lens technique in which light collection characteristics vary depending on an alignment direction of a liquid crystal layer constituting the lens and polarization of incident light. By using this, the polarization condition of the light emitted from a 2D image display panel and incident on a polarization dependent liquid crystal lens layer is changed, so that the 2D or 3D image can be selectively displayed.
In particular, since a viewing distance is as short as about 35 to 40 cm in a 3D mobile display, a focal length of the lens array needs to be as short as about 1 mm or less. Therefore, a gap between the display panel and the lens array also needs to be reduced.
On the other hand, as one of the active lens techniques for 2D/3D image switching, in a liquid crystal lens technique, liquid crystals are aligned according to an electric field generated by electrodes patterned in a liquid crystal cell structure, and a refractive index profile in a form of a GRIN lens appears. Therefore, the 2D/3D image switching can be performed according to a voltage applied to the liquid crystal cell.
However, in the form of the lens array, an electric field profile is preferably formed between the electrodes, but such an electric field profile is not directly above the electrode, and thus, a dead zone occurs between the lens and the lens. Therefore, there is a problem in that a fill-factor is lowered.
In particular, in a case where the lens array structure is applied to a mobile display, since the viewing distance is short, the focal length needs to be short, and thus, the gap of the liquid crystal cells becomes very large. In this case, there is a problem in that a driving voltage and a response speed become large. In addition, generally, as the focal length becomes shorter, an aberration problem arises. In the case of a liquid crystal lens, it is very difficult to solve the aberration problem.
In order to solve these problems, a polarization dependent lens using a liquid crystal phase polymer has been proposed. The polarization dependent lens has a structure in which a liquid crystal phase polymer (reactive mesogen ('RM)) is aligned in the lens structure and is turned on/off according to the polarization of incident light.
In addition to the above-described polarization dependent lens, a polarization switching section capable of adjusting the polarization direction of incident light needs to be provided in order to configure the display. FIG. 1 is a cross-sectional diagram exemplarily illustrating a polarization dependent lens section and a polarization switching section in the related art. Referring to FIG. 1, in the structure in the related art, the polarization dependent lens section and the polarization switching section are separated. In this case, a gap caused by two glass substrates exists between the display panel and the lens.
In a case where the above-described polarization dependent lens is applied to a mobile display, the focal length of the lens needs to be 1 mm or less. As described above, in a case where the polarization dependent lens section and the polarization switching section are separated, the gap caused by two glass substrates exists. As a result, the structure in the related art in which the polarization dependent lens section and the polarization switching section are separated has a problem that it is difficult to apply the structure to a mobile display device.